Undead in Lorithandar come in four forms:
Once mortal spirits who refuse the embrace of Su-Lan may linger as incorporeal spirits called Ghosts. These undead spirits often linger near their place of death or bind to items or people from their life, unwilling to leave. Shaman may make arrangements with such spirits, or bind them forcibly into service.
Revenants are corpses animated by disembodied planar spirits. Revenants have no love for the living, and are most often constructed by use of Sorcery. Because the magic which binds them to the flesh is controlled by their necromantic masters they must obey unfailingly. Their eyes glow with a colored light indicating the planar realm powering the corpse. Green for Stygia, Red for Pandemonium, Blue for Arcadia, and Gold for Aaru.
The Goddess of Death, Su-Lan may also answer supplications by her followers to return a fallen mortal soul by allowing the spirit to animate a Revenant. The spirit will serve the goddess and her servants unfailingly.
Native Outsiders of the dark plane of Stygia are sentient and powerful forms of undead. The entire realm of Stygia radiates necrotic energies which empower these beings. They may be enticed or forced through the Barrier with summon spells, but they are most certainly not benign and will only obey if bound into service. Trusting such a creature would be beyond foolhardy. The energies that empower the natives of Stygia has also been harnessed by powerful mortal sorcerers to grant them a demonic unlife… immortal, but twisted.
Lichborne are beings who have voluntarily transformed themselves into immortal undead upon reaching maturity. This practice is most common among the mixed-breed Human/Wild Elf Devinites of Karn, or by those Wild Elves who reside in Elarum. Newly transformed Lichborne appear as pale, cold, humanoids. However, the older they get, the more their corporeal form breaks down, eventually becoming entirely skeletal.